1 files changed, 169 insertions, 0 deletions
diff --git a/xpcom/base/nsMaybeWeakPtr.h b/xpcom/base/nsMaybeWeakPtr.h
new file mode 100644
index 0000000000..0566624265
--- /dev/null
+++ b/xpcom/base/nsMaybeWeakPtr.h
@@ -0,0 +1,169 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsMaybeWeakPtr_h_
+#define nsMaybeWeakPtr_h_
+
+#include "mozilla/Attributes.h"
+#include "mozilla/Try.h"
+#include "nsCOMPtr.h"
+#include "nsIWeakReferenceUtils.h"
+#include "nsTArray.h"
+#include "nsCycleCollectionNoteChild.h"
+
+// nsMaybeWeakPtr is a helper object to hold a strong-or-weak reference
+// to the template class.  It's pretty minimal, but sufficient.
+
+template <class T>
+class nsMaybeWeakPtr {
+ public:
+  nsMaybeWeakPtr() = default;
+  MOZ_IMPLICIT nsMaybeWeakPtr(T* aRef) : mPtr(aRef), mWeak(false) {}
+  MOZ_IMPLICIT nsMaybeWeakPtr(const nsCOMPtr<nsIWeakReference>& aRef)
+      : mPtr(aRef), mWeak(true) {}
+
+  nsMaybeWeakPtr<T>& operator=(T* aRef) {
+    mPtr = aRef;
+    mWeak = false;
+    return *this;
+  }
+
+  nsMaybeWeakPtr<T>& operator=(const nsCOMPtr<nsIWeakReference>& aRef) {
+    mPtr = aRef;
+    mWeak = true;
+    return *this;
+  }
+
+  bool operator==(const nsMaybeWeakPtr<T>& other) const {
+    return mPtr == other.mPtr;
+  }
+
+  nsISupports* GetRawValue() const { return mPtr.get(); }
+  bool IsWeak() const { return mWeak; }
+
+  const nsCOMPtr<T> GetValue() const;
+
+ private:
+  nsCOMPtr<nsISupports> mPtr;
+  bool mWeak;
+};
+
+// nsMaybeWeakPtrArray is an array of MaybeWeakPtr objects, that knows how to
+// grab a weak reference to a given object if requested.  It only allows a
+// given object to appear in the array once.
+
+template <class T>
+class nsMaybeWeakPtrArray : public CopyableTArray<nsMaybeWeakPtr<T>> {
+  typedef nsTArray<nsMaybeWeakPtr<T>> MaybeWeakArray;
+
+  nsresult SetMaybeWeakPtr(nsMaybeWeakPtr<T>& aRef, T* aElement,
+                           bool aOwnsWeak) {
+    nsresult rv = NS_OK;
+
+    if (aOwnsWeak) {
+      aRef = do_GetWeakReference(aElement, &rv);
+    } else {
+      aRef = aElement;
+    }
+
+    return rv;
+  }
+
+ public:
+  nsresult AppendWeakElement(T* aElement, bool aOwnsWeak) {
+    nsMaybeWeakPtr<T> ref;
+    MOZ_TRY(SetMaybeWeakPtr(ref, aElement, aOwnsWeak));
+
+    MaybeWeakArray::AppendElement(ref);
+    return NS_OK;
+  }
+
+  nsresult AppendWeakElementUnlessExists(T* aElement, bool aOwnsWeak) {
+    nsMaybeWeakPtr<T> ref;
+    MOZ_TRY(SetMaybeWeakPtr(ref, aElement, aOwnsWeak));
+
+    if (MaybeWeakArray::Contains(ref)) {
+      return NS_ERROR_INVALID_ARG;
+    }
+
+    MaybeWeakArray::AppendElement(ref);
+    return NS_OK;
+  }
+
+  nsresult RemoveWeakElement(T* aElement) {
+    if (MaybeWeakArray::RemoveElement(aElement)) {
+      return NS_OK;
+    }
+
+    // Don't use do_GetWeakReference; it should only be called if we know
+    // the object supports weak references.
+    nsCOMPtr<nsISupportsWeakReference> supWeakRef = do_QueryInterface(aElement);
+    if (!supWeakRef) {
+      return NS_ERROR_INVALID_ARG;
+    }
+
+    nsCOMPtr<nsIWeakReference> weakRef;
+    nsresult rv = supWeakRef->GetWeakReference(getter_AddRefs(weakRef));
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    if (MaybeWeakArray::RemoveElement(weakRef)) {
+      return NS_OK;
+    }
+
+    return NS_ERROR_INVALID_ARG;
+  }
+};
+
+template <class T>
+const nsCOMPtr<T> nsMaybeWeakPtr<T>::GetValue() const {
+  if (!mPtr) {
+    return nullptr;
+  }
+
+  nsCOMPtr<T> ref;
+  nsresult rv;
+
+  if (mWeak) {
+    nsCOMPtr<nsIWeakReference> weakRef = do_QueryInterface(mPtr);
+    if (NS_WARN_IF(!weakRef)) {
+      return nullptr;
+    }
+    ref = do_QueryReferent(weakRef, &rv);
+    NS_WARNING_ASSERTION(NS_SUCCEEDED(rv) || rv == NS_ERROR_NULL_POINTER,
+                         "QueryReferent failed with non-null pointer");
+  } else {
+    ref = do_QueryInterface(mPtr, &rv);
+    NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                         "QueryInterface failed with non-null pointer");
+  }
+  return ref;
+}
+
+template <typename T>
+inline void ImplCycleCollectionUnlink(nsMaybeWeakPtrArray<T>& aField) {
+  aField.Clear();
+}
+
+template <typename E>
+inline void ImplCycleCollectionTraverse(
+    nsCycleCollectionTraversalCallback& aCallback,
+    nsMaybeWeakPtrArray<E>& aField, const char* aName, uint32_t aFlags = 0) {
+  aFlags |= CycleCollectionEdgeNameArrayFlag;
+  size_t length = aField.Length();
+  for (size_t i = 0; i < length; ++i) {
+    CycleCollectionNoteChild(aCallback, aField[i].GetRawValue(), aName, aFlags);
+  }
+}
+
+// Call a method on each element in the array, but only if the element is
+// non-null.
+
+#define ENUMERATE_WEAKARRAY(array, type, method)                          \
+  for (uint32_t array_idx = 0; array_idx < array.Length(); ++array_idx) { \
+    const nsCOMPtr<type>& e = array.ElementAt(array_idx).GetValue();      \
+    if (e) e->method;                                                     \
+  }
+
+#endif